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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Deepwater Depositional Processes and Stratigraphy
of the Atlanta Field: Santos Basin, Block BS-4,
Offshore Brazil
Shell
Brazil Deepwater Development Team
Houston, Texas
The Atlanta Field, located in the northern Santos Basin,
offshore Brazil, is a world-class turbidite reservoir with over
1.5 billion barrels of heavy oil in place. The 115 meter thick, high
net-to-gross reservoir, exhibits porosities over 35% along with
multi-darcy permeability. The Eocene age, shallow reservoir
(-2400 m) is well imaged on 3-D seismic
, including a “textbook
quality”
seismic
flat-spot defining the oil-water contact. The field
was discovered in 2001 and has been appraised with three
additional well bores. An additional appraisal well followed by a
phased development is currently planned.
The Atlanta reservoir is part of a 600 km2 channelized slope
apron complex deposited on a stepped-slope topography during
the Eocene. The slope apron was fed through several southeasttrending
slope channels and is interpreted to have been sourced
by the collapse of nearby shelf-margin deltas. Within the lower
reservoir section, seismic
interpretation
reveals a broad incised
valley with nearly 100% net-to-gross sand fill. Within that incised
valley fill, stratal slicing shows systematic migration patterns that
are more often seen in steeper slope channels and are unusual in
a low-gradient and sand-rich setting. These pass upward into
more distributary channel and lobate forms. Well
data
show a
corresponding split between lower massive sands and an upper
more heterogeneous section characterized by the occurrence of
shale-clast conglomerate layers within high-quality sands.
Despite the good reservoir quality, development of this reservoir
presents challenges due to the viscous crude. A detailed
understanding of structural and stratigraphic heterogeneity is
required in order to reduce uncertainty in reservoir performance.
To achieve this, a data
acquisition and integrated
interpretation
program was conducted as part of field appraisal.
Interpretation
of reprocessed 3-D
seismic
to enhance stratigraphic detail, from
sub-regional down to
seismic
loop scale, has enabled a detailed
interpretation
of the geometry of this channelized apron. The
observations suggest that the system was overall strongly
aggradational, consisting of a limited number of channel and
lobate elements. Use of borehole image logs calibrated to limited
cores and coupled with a database of outcrop and subsurface
analogs allows for subsurface recognition and quantification
of potential baffles and barriers to flow within the reservoir. Our
integrated subsurface
interpretation
approach provides a
framework for generating multiple scenarios of the reservoir
architecture and spatial distribution of key heterogeneities in the
static models that will be used to forecast reservoir performance
in this sand-rich turbidite system.
3-D perspective showing
seismic
amplitude on the base Eocene structural surface. Warm colors depict areas of sandy turbidite apron accumulation
downdip of their slope feeder canyons. Inset well log depicts the Atlanta reservoir interval in the 3-SHEL-008-RJS appraisal well